title: Pediatric radiation dosimetry for positron-emitting radionuclides using anthropomorphic phantoms.
abstract: OBJECTIVE
  Positron emission tomography (PET) plays an important role in the diagnosis, staging, treatment, and surveillance of clinically localized diseases. Combined PET/CT imaging exhibits significantly higher sensitivity, specificity, and accuracy than conventional imaging when it comes to detecting malignant tumors in children. However, the radiation dose from positron-emitting radionuclide to the pediatric population is a matter of concern since children are at a particularly high risk when exposed to ionizing radiation.
  
  
  METHODS
  The authors evaluate the absorbed fractions and specific absorbed fractions (SAFs) of monoenergy photons/electrons as well as S-values of 9 positron-emitting radionuclides (C-11, N-13, O-15, F-18, Cu-64, Ga-68, Rb-82, Y-86, and I-124) in 48 source regions for 10 anthropomorphic pediatric hybrid models, including the reference newborn, 1-, 5-, 10-, and 15-yr-old male and female models, using the Monte Carlo N-Particle eXtended general purpose Monte Carlo transport code.
  
  
  RESULTS
  The self-absorbed SAFs and S-values for most organs were inversely related to the age and body weight, whereas the cross-dose terms presented less correlation with body weight. For most source/target organ pairs, Rb-82 and Y-86 produce the highest self-absorbed and cross-absorbed S-values, respectively, while Cu-64 produces the lowest S-values because of the low-energy and high-frequency of electron emissions. Most of the total self-absorbed S-values are contributed from nonpenetrating particles (electrons and positrons), which have a linear relationship with body weight. The dependence of self-absorbed S-values of the two annihilation photons varies to the reciprocal of 0.76 power of the mass, whereas the self-absorbed S-values of positrons vary according to the reciprocal mass.
  
  
  CONCLUSIONS
  The produced S-values for common positron-emitting radionuclides can be exploited for the assessment of radiation dose delivered to the pediatric population from various PET radiotracers used in clinical and research settings. The mass scaling method for positron-emitters can be used to derive patient-specific S-values from data of reference phantoms.
authors.affiliation: Division of Nuclear Medicine and Molecular Imaging, Geneva University Hospital, CH-1211 Geneva 4, Switzerland.
authors.forename: Tianwu
authors.initials: T
authors.lastname: Xie
authors.forename: Wesley E
authors.initials: WE
authors.lastname: Bolch
authors.forename: Choonsik
authors.initials: C
authors.lastname: Lee
authors.forename: Habib
authors.initials: H
authors.lastname: Zaidi
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D009010:Monte Carlo Method; D009928:Organ Specificity; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000295:instrumentation*; D011829:Radiation Dosage; D011874:Radiometry / Q000295:instrumentation*